Centrifugal oil pump for a variable speed hermetic compressor

ABSTRACT

Centrifugal oil pump for variable speed hermetic compressors, comprising: a hermetic shell (1), which lodges therewithin, a cylinder block (3), supporting a vertical eccentric shaft (5), whereto is mounted the rotor (8) of an electric motor (6), the eccentric shaft (5) being provided with at least one oil channel (9), having a lower end (9b), opened to a lower end (5b) of the eccentric shaft (5), wherein the eccentric shaft-rotor assembly attaches, at its lower part, an upper extension (12) of a pump rotor (10) and a tubular sleeve (20), attached to an inertial portion of the compressor and surrounding at least the portion of said pump rotor (10) external to the rotor (8), said pump rotor (10) presenting a centrifugation region (15), radially extending beyond the edges of the lower end (5b) of the eccentric shaft (5) and having a lower end nozzle (10b) that is permanently immersed in the oil sump (2), which is internally defined at the bottom of the shell (1) and with at least an upper radial nozzle (11b), communicating with at least an oil conducting axial channel (18), which communicated with the lower end of the oil channel (9) through at least one dragging duct (14), which is longitudinally provided through the upper extension (12) of the pump rotor (10).

FIELD OF THE INVENTION

The present invention refers to an oil pump for variable speed hermeticcompressors of the reciprocating type, particularly those having avertical shaft and used in refrigerators and freezers.

BACKGROUND OF THE INVENTION

These appliances require that their respective hermetic compressorssupply the exact refrigerating capacity necessary to remove the internalheat from the medium to be refrigerated. As the refrigerating capacityis proportional to the flow of the refrigerant mass pumped by thecompressor, a variation of the refrigerating capacity is related to avariation of the mass flow pumped by the compressor. A technique ofcontinuously obtaining said variation in the refrigerant mass flow is byvarying the motor speed.

There are studies indicating that the variable speed compressors need anoperative range from 15Hz to 100Hz, i.e., speeds between 900 and 6000rpm, in order to achieve a good refrigerating performance. Such speedvariation affects the mechanical operation of the compressor, especiallythe operation of the oil pump, which conducts the oil to the bearings ofthe compressor mechanism and other regions in need of lubrication, suchas the connecting rod and piston.

Centrifugal pumps are the oil pumping mechanisms most used in hermeticcompressors, both for their relatively low cost and adequate operationin 3000 rpm up to 3600 rpm rotation range, which result from thefrequency of the electrical network. Nevertheless, such mechanismsbecome inoperative at low rotation speeds.

Conventional oil pumps of the centrifugal type, such as the oneillustrated in FIG. 1 and presently in use, are not capable of pumpingthe oil to the bearings when the compressor needs to operate at lowspeeds.

The operative limitations of the centrifugal pump are related to thedifference between its larger radius (R) and its smaller radius (r), asshown in the equation below, which governs the behavior of thecentrifugal pump:

    ω= (2×g×h)/(R.sup.2 -r.sup.2)!.sup.1/2

where h is the required pumping height from the oil level up to thebearings; g is the gravitational constant; R is the larger radius of thepump; r is the smaller radius; and ω is the angular speed (rd/sec). Thesearch for an increase in the oil pumping efficiency in such compressorsby simply increasing the larger radius (R) of the pump is unfeasible,because such increase, which is necessarily substantial to achieve thedesired pumping, also affects the external diameter of the compressorshaft and, consequently, all of the manufacturing processes of thecompressor and the performance thereof, since it causes greater lossesdue to friction. It should be observed that small diameter alterationsare not enough to achieve the necessary degree of centrifugal pumping atrotational speeds close to or lower than 900 rpm.

Conventional centrifugal pumps which have a vertical or a horizontalshaft are widely used in hermetic compressors, as evidenced by thepatent documents U.S. Pat. No. 4,478,559; U.S. Pat. No. 4,569,639; DT209,877 and FR 2,492,471. Nevertheless, said centrifugal pumps do notwork, or work inefficiently, at rotational speeds lower than about 900rpm.

In another solution, described in a copending patent application of thesame applicant, the increase in the pumping efficiency is achievedthrough a pump rotor having ascending helical grooves which are providedalong a portion of the outer surface of the longitudinal extension ofsaid rotor. This solution, though presenting an efficient lubrication atrotational speeds (600 rpm) lower than those reached with conventionaloil pumps, achieves its pumping effect by mechanically moving the oilalong the helical grooves of the pump rotor.

OBJECT OF THE INVENTION

Thus, it is an object of the present invention to provide a centrifugaltype oil pump for variable speed reciprocating hermetic compressorshaving a vertical shaft, in which the pumping performance is similar tothat obtained with pumps using mechanical movement of the oil at lowrotational speeds, e.g., about 600 rpm.

A second object of the present invention is to provide an oil pump asmentioned above, whose pumping capacity is increased, withoutconstructive alterations or redimensionings of the cylinder blockcomponents.

A third object of the present invention is to provide an oil pump ofsimple manufacture and assembly.

A fourth object of the present invention is to provide an oil pump thatdoes not generate oil whirl in the sump of the compressor, as occurswith some conventional centrifugal oil pumps.

BRIEF DESCRIPTION OF THE INVENTION

These and other objectives and advantages are attained from an oil pumpfor a variable speed hermetic compressor of the type including the oilpump of the present invention. Such oil pump includes a hermetic shell,which defines a lubricant oil sump at its bottom and which lodgestherewithin; and a cylinder Block which supports a vertical eccentricshaft to which is mounted a rotor of an electric motor. The eccentricshaft is provided with at least one oil channel having a lower endopened to the lower end of the eccentric shaft and an upper end openedto the external part of the upper median portion of the eccentric shaft.The eccentric shaft-rotor assembly has attached at its lower part anupper extension of a pump rotor and a tubular sleeve attached to aninertial portion of the compressor and surrounding at least the portionof said pump rotor external to the rotor. The pump rotor has at aportion of its extension external to the rotor a centrifugation regionradially extending beyond the lower end edges of the eccentric shaft andhaving a lower end nozzle that is permanently immersed in the oil sumpand in permanent fluid communication with at least an upper radialnozzle that communicates with at least one oil conducting axial channeldefined between the peripheral surface of said portion of the pump rotorexternal to the rotor and a respective angular sector of the adjacentinternal wall portion of the tubular sleeve. The oil conducting axialchannel communicates with the lower end of the oil channel through atleast one oil dragging duct, which is longitudinally provided throughthe upper extension of the pump rotor.

The oil pump as described above has the advantage of not depending uponthe physical dimensions of the compressor, wherein the minimum rotationspeed (e.g., 600 rpm) is easily obtained by adjusting the diameter ofthe pump rotor. The oil pump may also be used at rotation speeds above6000 rpm without impairing its operation and allowing its application incompressors mounted in the conventional manner, i.e., with the motor atthe lower part of the body.

DETAILED DESCRIPTION OF THE INVENTION

The invention will be described below, with reference to the attacheddrawings, in which:

FIG. 1 illustrates a prior art oil pump, in a longitudinal diametralsection view, mounted inside a hermetic compressor and showing thedimensions h₁, h₂, R and r;

FIGS. 2a and 2b illustrate, respectively, an enlarged view of a priorart oil pump, during the oil pumping at a normal angular speed (2a) andat a reduced speed (2b);

FIG. 3 illustrates in a longitudinal view the inside of a hermeticcompressor with an oil pump of the present invention; and

FIG. 4 is an enlarged cross sectional view of the oil pump of thepresent invention.

BEST MODE OF CARRYING OUT THE INVENTION

According to the drawing figures described above, a variable speedhermetic compressor of the vertical shaft type includes a hermetic shell1, defining a lubricant oil sump 2 at its bottom. A cylinder block 3within the shell incorporating a bearing 4 for supporting a verticaleccentric shaft 5 having an upper end 5a and a lower end 5b. An electricmotor 6 having a stator 7 is attached to the cylinder block 3 and arotor 8 is attached to a portion of the eccentric shaft 5 located belowthe bearing 4 and defining an eccentric shaft-rotor assembly. Theeccentric shaft 5 is provided with at least one oil channel 9, having alower end 9b opened to the lower end 5b of the eccentric shaft 5 and anupper end 9a opened to the external part of the upper median portion ofthe eccentric shaft 5 at the region of the bearing 4. The eccentricshaft 5 has fitted at its lower end 5b an upper end 10a of a centrifugalpump rotor 10, whose lower end nozzle 10b is immersed in the oil massprovided in the sump 2.

In these compressors, as illustrated in FIGS. 2a and 2b, the lubricationof the bearings and other components is made through centrifugationduring the rotation of the eccentric shaft-rotor assembly, the rotationspeed being about 3000-3600 rpm during the normal operation of thecompressor.

Nevertheless, at low rotation speeds, usually lower than 2000 rpm, thelubrication of the components becomes marginal, or occasionally does notexist at all, since the oil column formed by the centrifugal effectinside the oil channel 9 no longer reaches the upper end 9a of the oilchannel 9.

In such compressors, the efficiency of the oil pump is a function of therelation between its smaller diameter (radius r), immersed in the sump2, and its larger diameter (radius R). The closer said values, the lesswill be the lubrication force of said oil pump, as mentioned above.

According to the present invention and as shown in FIG. 3, the increaseof the pumping capacity for centrifugal oil pumps is achieved with anincrease of the difference between said smaller radius r, relative tothe opening of the lower end nozzle 10b for the entrance of oil into thepump rotor 10, and a larger radius R, of maximum spacing from thegeometric axis of the oil pump. This larger radius R is defined by theextension of at least one radial channel 11, which is preferablyorthogonal to the lower end nozzle of the oil inlet 10b and whichcommunicates the oil received from the sump 2 by said lower end nozzle10b with an oil receiving region as described below.

In another possible construction, said radial channel 11 is upwardlyinclined from the lower end nozzle 10b of the pump rotor 10.

The pump rotor of the present invention has an attaching upper portion12, in the form of a retaining cylindrical head, and a tubular sleeve20. The attaching head 12 avoids the relative movement between the pumprotor 10 and the eccentric shaft-rotor assembly, due to the pressureexerted by the lateral walls of said head 12 against the internal wallof an axial housing defined at the lower end 5b of the eccentric shaft5, or at the lower portion of an axial central bore of the rotor 8, whenthe eccentric shaft 5 does not reach the lower face of the rotor 8.

According to the present invention, said head 12 has adjacent to thelower portion thereof a round peripheral groove 13, which is concentricwith the geometric axis of said pump rotor 10 and which defines an oilring together with the adjacent internal wall of the tubular sleeve 20and whereon the oil pumped from the sump 2 is continuously deposited inorder to be sent to the oil channel 9.

The fluid communication between said peripheral groove 13 and the oilchannel 9 is made through a dragging duct 14, with an "L" shape andprovided inside the head 12, in such a way as to present a small radialextension thereof connected to a central axial extension for oilelevation. Said dragging duct 14 has an oil outlet upper end 14a, openedto the inside of the oil channel of the eccentric shaft 5, and an oilinlet lower end 14b, opened to the peripheral groove 13, whichcommunicates with an oil duct, to be described below, and where the oilcentrifugated from the sump 2 is deposited before being conducted to theoil channel 9, without power loss.

In another possible embodiment, the peripheral groove 13 is provided atan angular sector in the periphery of the head 12, where the lower end14b of the dragging duct 14 is located. In either of the embodimentsdescribed above, said peripheral groove 13 may optionally surround theexternal wall of said head 12, till reaching said lower end 14b of thedragging duct 14, following an upward helical path that does not surpassthe lower end of the shaft. In this case, for the purpose of oildragging, said helical groove should be provided at the portion of thehead 12 in contact with the internal walls of the tubular sleeve 20,occupying an angular extension of the peripheral wall of said head 12and defined dimensionally in accordance with the desired oil amount tobe supplied to the oil channel 9.

Though not illustrated, in another embodiment the dragging duct 14 maybe in the form of at least an external longitudinal slot extending fromthe peripheral groove 13 up to the upper end 10a of the pump rotor 10.In an alternative of this solution, the head 12 is provided with aplurality of dragging ducts 14, longitudinally crossing the inside ofsaid head and forming a diverging ascending bundle of ducts. In anotheralternative, the head 12 maintains a fluid communication between theperipheral groove 13 and the oil channel 9, through a combination ofdragging ducts and peripheral slots.

The pump rotor 10 further includes a centrifugation lower portion,comprising a centrifugation base 15, which is preferably round and flatand which incorporates at its center, from the upper face thereof, thehead 12 and, aligned with the latter, from the lower face of said roundbase 15, a pumping tubular duct 16, in the form of a tubular conductorthat is constantly immersed in the oil sump 2 and through which the oilis led to the radial channel 11. Said tubular duct 16 presents an upperopening 16a, communicating the lower nozzle 10b of the pump rotor 10with the radial channel 11. Said radial channel 11 has an external end11b spaced from the lower edge of the round base 15, so as to define,together with the tubular sleeve 20, an oil distribution annular duct17, where the centrifugated oil is continuously deposited in the sump 2.

The portion of the pump rotor 10, external to the eccentric shaft 5, issurrounded by the tubular sleeve 20, attached to a portion of thecompressor, for example, to the shell thereof, so as not to rotate withsaid pump rotor 10. This attachment can be made such as described in PI9201761 (WO 93/22557). In the illustrated embodiment, said attachment ismade through an attaching arm 50, attached to an inertial portion of thecompressor, such as the shell 1 thereof.

The tubular sleeve 20 has an upper opening 20a, facing the lower end 5bof the eccentric shaft 5 and having its diameter matching the diameterof the lower end 9b of the oil channel 9, which communicates with alower opening 20b, of a diameter that is slightly larger than thediameter of the corresponding basic portion 15 of the pump rotor 10.Said lower opening 20b faces the sump 2, and it may have its end edgepermanently spaced from the oil located in said sump 2. The tubularsleeve 20 is kept constantly spaced from the pump rotor 10, therebycreating a minimum radial gap from the latter, said gap being necessaryto prevent said tubular sleeve 20 from rotating together with theeccentric shaft-rotor assembly and thus eliminating the oil draggingoperation.

Though not illustrated, the upper end 20a of the tubular sleeve 20 maybe introduced into the axial housing, such as in the patent documentcited above, if a portion of the head 12, which is not attached to saidaxial housing, comprises peripheral grooves that develop helically atthis region. The edge of the upper opening 20a of said sleeve 20 ispositioned relative to the eccentric shaft 5, slightly spaced therefrom,thereby allowing the presence at the region therebetween of a finelubricating oil film, that avoids the contact wear of said parts duringthe rotation of the eccentric shaft-rotor assembly.

In the present embodiment, the lower opening 20b of the tubular sleeve20 is defined at an internal body portion of said sleeve 20 in the formof a peripheral skirt, whose walls are parallel to the walls of thelower end 5b of the eccentric shaft 5, defining an external wall of saidoil distribution annular duct 17. From a portion of said annular duct17, there is extended, preferably longitudinally relative to saidperipheral skirt, a lubricant fluid ascending channel 18, communicatingthe centrifugated oil through the radial channel 11, with the oil inlet14b of the dragging duct 14 of the head 12. This ascending channel isdefined by a recessed portion of the internal wall of the tubular sleeve20, having a width at least matching with the diameter of the channel11, in order not to cause the saturation of the oil annular duct 16 andthe consequent oil return to the sump 2, thereby reducing the pumpingefficiency.

During the oil pumping operation, the pump rotor 10 carries bycentrifugation the oil from the sump 2 to the channel 11, where, due tothe increase of the radius R, said oil is directed to the oil duct 17with a power increase which is maintained, without significant losses,till said oil mass reaches the upper end 10a of the pump rotor 10, thenpassing to the oil channel 9.

We claim:
 1. Centrifugal oil pump for a hermetic compressor comprising:ahermetic shell which defines a lubricant oil sump at its bottom; acylinder block in said shell which supports a vertical shaft mounted toa rotor of an electric motor, the shaft having at least one internal oilchannel with a lower end at the lower end of the shaft and an upper endwith an opening to the shaft exterior at a point between the upper andlower ends of the shaft; a an upper extension of a pump rotor having anupper part within said shaft lower end and a lower part extending belowsaid shaft lower end and a tubular sleeve attached to a fixed portion ofthe compressor, said tubular sleeve surrounding at least said lower partof said upper extension external to the shaft; said pump rotor having acentrifugation region radially extending beyond the edges of the lowerend of said shaft and a nozzle at its lower end that is immersed in theoil sump and in fluid communication with at least an upper radial nozzlethat communicates with at least an oil conducting axial channel betweenthe peripheral surface of said portion of the pump rotor external to theshaft and a respective angular sector of the adjacent internal wallportion of said tubular sleeve, said oil conducting axial channelcommunicating with the lower end of said shaft oil channel through atleast one dragging duct which is longitudinally provided through theupper extension of the pump rotor.
 2. Oil pump, according to claim 1,wherein said oil conducting axial channel is defined by a recess in thecorresponding adjacent internal wall portion of said tubular sleeve. 3.Oil pump, according to claim 2, wherein said oil conducting axialchannel communicates with an oil distributing annular duct between theoutside of said pump rotor and said tubular sleeve, said duct being influid communication with said upper radial nozzle.
 4. Oil pump,according to claim 2, wherein said centrifugation region is defined by aflat round base having upper and lower peripheral edges and having atleast one internal radial channel providing communication between thelower end nozzle and the upper radial nozzle.
 5. Oil pump, according toclaim 4, wherein said at least one radial channel is orthogonal to theshaft.
 6. Oil pump, according to claim 1, wherein said oil conductingaxial channel communicates with the shaft oil channel through at leastone dragging duct in said upper part of said pump rotor upper extension.7. Oil pump, according to claim 6, wherein the oil dragging duct has anaxial central portion in said pump rotor with an upper end opened to theshaft oil channel and at least one radial lower end opened to the oilconducting axial channel.
 8. Oil pump, according to claim 7, wherein thelower end of each said dragging duct is opened to a peripheral annularoil duct on said lower part of said upper extension of said pump rotor.9. Oil pump according to claim 1, wherein the radius of the opening ofthe nozzle at said lower end of said centrifugation region is smallerthan the radius of said centrifugation region.